This application disclosed an inention that is related, generally and in various embodiments, to an intergrated power cell bypass assembly, and a power supply including same.
In certain applications, multi-cell power supplies utilize modular power cells to process power between a source and a load. Such modular power cells can be applied to a given power supply with various degrees of redundancy to improve the availability of the power supply. For example, FIG. 1 illustrates various embodiments of a power supply (e.g., an AC motor drive) having nine such power cells. The power cells in FIG. 1 are represented by a block having input terminals A, B, and C; and output terminals T1 and T2. In FIG. 1, a transformer or other multi-winding device 110 receives three-phase, medium-voltage power at its primary winding 112, and delivers power to a load 130 such as a three-phase AC motor via an array of single-phase inverters (also referred to as power cells). Each phase of the power supply output is fed b a group of series-connected power cells, called herein a “phase-group”. As shown in FIG. 1, according to various embodiments, the primary winding 112 may receive its power via a main contactor 111. The main contactor 111 ma be embodied as a vacuum contactor.
The transformer 110 includes primary windings 112 that excite a number of secondary windings 114-122. Although primary winding 112 is illustrated as having a star configuration, a mesh configuration is also possible. Further, although secondary windings 114-122 are illustrated as having a delta or an extended-delta configuration, other configurations of windings may be used as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety. In the example of FIG. 1 there is a separate secondary winding for each power cell. However, the number of power cells and/or secondary windings illustrated in FIG. 1 is merely exemplary, and other numbers are possible. Additional details about such a power supply are disclosed in U.S. Pat. No. 5,625,545.
Any number of ranks of power cells are connected between the transformer 110 and the load 130. A “rank” in the context of FIG. 1 is considered to be a three-phase set, or a group of three power cells established across each of the three phases of the power delivery system. Referring to FIG. 1, rank 150 includes power cells 151-153, rank 160 includes power cells 161-163, and rank 170 includes power cells 171-173. A master control system 195 sends command signals to local controls in each cell over fiber optics or another wired or wireless communications medium 190. It should be noted that the number of cells per phase depicted in FIG. 1 is exemplary, and more than or less than three ranks may be possible in various embodiments.
FIG. 2 illustrates various embodiments of a power cell 210 which is representative of various embodiments of the power cells of FIG. 1. The power cell 210 includes a three-phase diode-bridge rectifier 212, one or more direct current (DC) capacitors 214, and an N-bridge inverter 216. The rectifier 212 converts the alternating current (AC) voltage received at cell input 218 (i.e., at input terminals A, B and C) to a substantially constant DC voltage that is supported by each capacitor 214 that is connected across the output of the rectifier 212. The output stage of the power cell 210 includes an H-bridge inverter 216 which includes two poles, a left pole and a right pole, each with two switching devices. The inverter 216 transforms the DC voltage across the DC capacitors 214 to an AC output at the cell output 220 (i.e., across output terminals T1 and T2) using pulse-width modulation (PWM) of the semiconductor devices in the H-bridge inverter 216.
As shown in FIG. 2, the power cell 210 may also include fuses 222 connected between the cell input 218 and the rectifier 212. The fuses 222 may operate to help protect the power cell 210 in the event of a short-circuit failure. According to other embodiments, the power cell 210 is identical to or similar to those described in U.S. Pat. No. 5,986,909 and its derivative U.S. Pat. No. 6,222,284 to Hammond and Aiello, the disclosures of which are incorporated herein by reference in their entirety.
FIG. 3 illustrates various embodiments of a bypass device 230 connected to output terminals T1 and T2 of the power cell 210 of FIG. 2. In general, when a given power cell of a multi-cell power supply fails in an open-circuit mode, the current through all the power cells in that phase-group will go to zero, and further operation is not possible. A power cell failure may be detected by comparing a cell output voltage to the commanded output, by checking or verifying cell components, through the use of diagnostics routines, etc. In the event that a given power cell should fail, it is possible to bypass the failed power cell and continue to operate the multi-cell power supply at reduced capacity.
The bypass device 230 is a single pole single throw (SPST) contactor, and includes a contact 232 and a coil 234. As used herein, the term “contact” generally refers to a set of contacts having stationary portions and a movable portion. Accordingly, the contact 232 includes stationary portions and a movable portion which is controlled by the coil 234. The bypass device 230 may be installed as an integral part of a converter subassembly in a drive unit. In other applications the bypass device 230 may be separately mounted. When the movable portion of the contact 232 is in a bypass position, a shunt path is created between the respective output lines connected to output terminals T1 and T2 of the power cell 210. Stated differently, when the movable portion of the contact 232 is in a bypass position, the output of the failed power cell is shorted. Thus, when power cell 210 experiences a failure, current from other power cells in the phase-group can be carried through the bypass device 230 connected to the failed power cell 210 instead of through the failed power cell 210 itself.
FIG. 4 illustrates various embodiments of a different bypass device 240 connected to output terminals T1 and T2 of the power cell 210. The bypass device 240 is a single pole double throw (SPDT) contactor, and includes a contact 242 and a coil 244. The contact 242 includes stationary portions and a movable portion which is controlled by the coil 244. When the movable portion of the contact 242 is in a bypass position, one of the output lines of the power cell 210 is disconnected (e.g., the output line connected to output terminal T2 in FIG. 4) and a shunt path is created between the output line connected to output terminal T1 of the power cell 210 and a downstream portion of the output line connected to output terminal T2 of the power cell 210. The shunt path carries current from other power cells in the phase group which would otherwise pass through the power cell 210. Thus, when power cell 210 experiences a failure, the output of the failed power cell is not shorted as is the case with the bypass configuration of FIG. 3.
The bypass devices shown in FIGS. 3 and 4 do not operate to disconnect power to any of the input terminals A, B or C in the event of a power cell failure. Thus, in certain situations, if the failure of a given power cell is not severe enough to cause the fuses 222 (see FIG. 2) to disconnect power to any two of input terminals A, B or C, the failure can continue to cause damage to the given power cell.
FIG. 5 illustrates various embodiments of a system 250 for bypassing a power cell (e.g. power cell 210) of a power supply. As shown in FIG. 5, the system 250 includes bypass device 252 connected to the output terminals T1 and T2, a bypass device 254 connected to input terminal A, and a bypass device 256 connected to input terminal C. Although the system 250 is shown in FIG. 5 as having respective bypass devices connected to input terminals A and C, it will be appreciated that, according to other embodiments, the respective bypass devices may be connected to any two of the input terminals A, B and C. In various implementations, the bypass devices 252, 254, 256 may be mechanically-driven, fluid-driven, electrically-driven, or solid state, as is described in the '909 and '284 patents.
According to various embodiments, bypass device 252 is a single pole double throw (SPDT) contactor, and includes a contact 258 and a coil 260. The contact 258 includes stationary portions and a movable portion which is controlled by the coil 260. The bypass device 252 operates in a manner similar to that described hereinabove with respect to bypass device 240 of FIG. 4. The bypass device 254 is a single pole single throw (SPST) contactor, and includes a contact 262 and a coil 264. The contact 262 includes stationary portions and a movable portion which is controlled by the coil 264. The bypass device 256 is a single pole single throw (SPST) contactor, and includes a contact 266 and a coil 268. The contact 266 includes stationary portions and a movable portion which is controlled by the coil 268. In general, in the event of a failure, bypass devices 254, 256 disconnect the cell input power at substantially the same time that bypass device 252 creates a shunt path for the current that formerly passed through the failed power cell.
The condition associated with the creation of the described shunt path and the disconnection of cell input power from at least two of the cell input terminals may be referred to as “full-bypass”. When the full bypass condition is present, no further power can flow into the failed cell. As described with respect to FIG. 2, the fuses 222 of the power cell may operate to help protect the power cell in the event of a short-circuit failure. However, in certain situations (e.g., when the available fault current is low), the fuses 222 may not clear quickly enough to prevent further damage to the failed power cell. According to various embodiments, the bypass devices 254, 256 are configured to act quicker than the fuses 222, and the quicker action generally results in less damage to the failed power cell. According to various implementations, the main contactor 111 may interrupt power to the transformer 110 before the bypass devices 254, 256 act to disconnect the two power cell inputs.
FIG. 6 illustrates a simplified representation of various views (i.e. top, side and rear) of a power cell (e.g., power cell 210) of a power supply according to various embodiments. The power cell includes a plurality of fixed terminals 270 which serve as connection terminals for the power cell. The fixed terminals 270 may be embodied in any suitable shape or configuration. For purposes of simplicity, the fixed terminals 270 will be described hereinafter in the context of male stab plugs 270. With the male stab plugs 270, a failed power cell can be quickly and easily disconnected, removed, and replaced with another power cell. For the embodiments shown in FIG. 6, the power cell includes five male stab plugs 270 (see the rear view) which correspond to input terminals A, B and C and output terminals T1 and T2 of the power cell. According to other embodiments, the power cell may include more than or less than five male stab plugs 270, and the male stab plugs 270 may be shaped, located and/or arranged in a manner which is different than that shown in FIG. 6.
FIG. 7 illustrates a simplified representation of the power cell of FIG. 6 being installed in a power supply. For purposes of clarity, only a portion of the power supply is shown in FIG. 7. The power supply includes a plurality of fixed female receptacles 272 which correspond to and are respectively aligned with the male stab plugs 270, a first insulating member 274, and a second insulating member 276. As shown in FIG. 7, the first insulating member 274 is connected to the second insulating member 276, the fixed female receptacles 272 are connected to the first insulating member 274, and the second insulating member 276 supports the weight of the power cell. As the power cell is moved toward the first insulating member 274, the male stab plugs 270 of the power cell respectively engage the corresponding fixed female receptacles 272 to form electrical connections. The fixed female receptacles 272 may be connected to other circuits via conductors 278 such as cables, bus bars, etc. Each male stab plug 270 and the corresponding fixed female receptacle 272 may collectively be considered a stab assembly.
In general, electrical contacts (e.g., bypass contacts 258, 262, 266 of FIG. 5) are less reliable than permanent connections such as cables or bus bars. For a given electrical contact, the contacting surfaces may become contaminated over time, thereby increasing the electrical resistance of the contact. The increased resistance may lead to higher operating temperatures while conducting current, which may accelerate the contamination process. Also, mechanical wear or misalignment may over time reduce the force holding the surfaces in contact, thereby leading to higher operating temperatures while conducting current. For similar reasons, stab connections such as those described with respect to the male stab plugs 270 and fixed female receptacles 272 also tend to be less reliable than permanent connections such as cables or bus bars.
For multi-cell power supplies or drives equipped with both cell bypass (e.g., full bypass as shown in FIG. 5) and stab connections (e.g., as shown in FIG. 7), the current into and out of the cell must generally flow through two sets of electrical contacts in series, namely the stab connections (i.e., the connections between the male stab plugs 270 and the corresponding fixed female receptacles 272) and the bypass contacts (i.e., contacts 258, 262, 266 of FIG. 5).